PROJECT SUMMARY/ABSTRACT Our laboratory?s overall goal is to determine the cellular and molecular mechanisms of gastrointestinal (GI) mechanosensitivity in normal GI physiology and in functional GI diseases, such as irritable bowel syndrome (IBS). Our K08-supported research focused on an important specialized epithelial mechanosensory cell, called enterochromaffin (EC) cell. In response to mechanical force, the EC cell releases serotonin, which has important physiologic effects and this mechanism, is disrupted in IBS. With K08 support, we discovered that a novel mechanosensitive ion channel Piezo2 is specifically expressed in mouse and human EC cells, and that Piezo2 activation leads to release of 5-HT and mechanically-induced epithelial secretion. The current work is aimed at understanding the molecular mechanism of EC cell mechanosensitivity downstream of Piezo2 channels. The experiments, while foundationally linked to previous work, are a new and logical extension of the work associated with the K08 and can be completed in the defined award period. The results from this study are important because they will define a novel mechanotransduction mechanism and allow us to deeply understand EC cell mechanosensation in health, which will enable us to examine alterations in disease, and then potentially target these pharmacologically as novel and specific therapies for IBS.